John's Geekblog

If you've come here to find another (?) exciting, sexy weblog full of observations both witty and meaningful, you've come to the wrong place. I don't have any reason to believe that you'd find anything in my life very interesting.

This blog has one simple purpose: to be my on-line logbook for data from my experiments in ham radio and time/frequency measurement. If you want to know when I last adjusted the frequency of my Rubidium standard, then this is the place to be. Otherwise, forget it.
jra on 08.03.03 @ 10:11 AM EST [link]

Sunday, February 26th

28 Volt Battery System Details

I am using two 100AH AGM batteries in series. using an IOTA DLS 27-15/IQ4 15 amp charger. The IOTA is an intelligent charger with three modes:

The board has a pre-regulator stage but using this requires significant headroom above the output voltage -- abiout 4 - 4.5 volts. Since the oscillator wants 24 volts and the system is run off of 2 "12V" AGM cells in series connected to a float charger, this doesn't allow for much drop if the power goes off and the batteries start to run down. The main advantage of the pre-regulator is to improve the dynamic stability of the system (ie, reduce the output voltage change when there is a sudden change of input voltage). That's not a major issue for this application since the OCXO will draw nearly constant power once it's warmed up. So, I am bypassing the pre-regulator stage to reduce the headroom requirement.

With a 28.8V input, the output voltage is 24.023 volts. Reducing the input voltage shows a very pronounced loss of regulation at about 24.5V, with about 0.1V reduction of the output over less than 0.1V change of the input. The voltage has been stable within +/-0.5 millivolt for 12 hours after initial power-on.

The circuit uses an LED which glows when the circuit is operating properly. The LED extinguishes at about the same point as regulation is lost, so it's a good reference point -- if the LED is fully lit, there's enough voltage to maintain regulation.

As a last bit of data, at 28.8V input, the regulator draws about 32ma with no load other than the DVM.